PATCH [v3 0/2] NFSD: use CB_GETATTR to handle GETATTR conflict with write delegation

[Dai Ngo <dai.ngo@oracle.com>]

Currently GETATTR conflict with a write delegation is handled by
recalling the delegation before replying to the GETATTR.

This patch series add supports for CB_GETATTR callback to get the latest
change_info and size information of the file from the client that holds
the delegation to reply to the GETATTR from the second client.

NOTE: this patch series is mostly the same as the previous patches which
were backed out when un unrelated problem of NFSD server hang on reboot
was reported.

The only difference is the wait_on_bit() in nfsd4_deleg_getattr_conflict was
replaced with wait_on_bit_timeout() with 30ms timeout to avoid a potential
DOS attack by exhausting NFSD kernel threads with GETATTR conflicts.

v2:
  . update comments in nfsd4_deleg_getattr_conflict

v3:
  . rebase with nfsd-next

 fs/nfsd/nfs4callback.c |  97 ++++++++++++++++++++++++++++++++++++-
 fs/nfsd/nfs4state.c    | 115 ++++++++++++++++++++++++++++++++++++++++----
 fs/nfsd/nfs4xdr.c      |  10 +++-
 fs/nfsd/nfsd.h         |   1 +
 fs/nfsd/state.h        |  24 ++++++++-
 fs/nfsd/xdr4cb.h       |  18 +++++++
 6 files changed, 251 insertions(+), 14 deletions(-)